The present invention relates to a transmitter for an amplitude modulated signal and, more particularly, to an Amplitude Modulation (AM) signal transmitter provided with a pulse width modulation system.
In a high power AM signal transmitter, it is an important requirement to improve power efficiency as much as possible, and, to this end, class D amplification or pulse width modulation is utilized. In one prior art system, the AM transmitter comprises a modulation amplifier and a modulated power amplifier in the final stage which are connected in series. Modulation amplifier is subject to pulse operation by a pulse width modulated signal. Another prior art AM transmitter is disclosed in UK Patent Application No. 2,079,105, whose modulation amplifier section is structured in a push-pull arrangement. However, in the prior art AM transmitters, a power supply source requires a voltage about twice that needed for operating the power amplifier of the final stage. Therefore, this leads to the disadvantages of a high cost and greater danger owing to the higher voltage.